1. Field of the Invention
This invention relates to wide-angle zoom lenses suited to cameras for photography, video cameras and SV (still video) cameras, etc. and, more particularly, to a wide-angle zoom lens having five lens units as a whole in which a lens unit of negative refractive power leads, the size of the entire lens system being made minimum by properly setting the lens arrangement of these five lens units.
2. Description of the Related Art
In a zoom lens of the so-called negative lead type in which a lens unit of negative refractive power leads, it is relatively easy to widen the angle of view. For this reason, the negative lead type has been used in many wide-angle zoom lenses having an angle of view of more than 70.degree.. For example, in Japanese Patent Publication No. Sho 49-23912, Japanese Laid-Open Patent Application No. Sho 57-163213, etc., there is proposed a zoom lens having four lens units, i.e., in the order from the object side, a first lens unit of negative refractive power, a second lens unit of positive refractive power, a third lens unit of negative refractive power and a fourth lens unit of positive refractive power, wherein when zooming from the wide-angle end to the telephoto end, the first lens unit is made to move toward the image side, the second lens unit and the fourth lens unit are made to move toward the object side, and the third lens unit is made to be stationary or to move.
Further, in, for example, Japanese Laid-Open Patent Application No. Sho 58-50327 and British Patent No. 398307, etc., there is proposed a zoom lens having three lens units, i.e., in the order from the object side, a first lens unit of negative refractive power, a second lens unit of positive refractive power and a third lens unit of negative refractive power, of which at least two lens units are made to move to perform variation of the magnification.
In general, in a zoom lens, a first lens unit on the object side is frequently made to be large in the lens outer diameter and in weight. Therefore, in a camera in which the operation of varying the magnification is manually performed, such as a single-lens reflex camera for 35 mm silver-halide film, even if the variation of the magnification is of the type that the first lens unit is moved when varying the magnification, there is not much problem on mechanism.
However, in a camera of the power zoom type in which variation of the magnification is performed by electric drive, such as a video camera, the type of magnification variation in which the first lens unit of large weight is moved when varying the magnification necessitates a drive means using an electric motor of large size, etc. Also, in the points of electric power consumption and space, a problem arises in that the whole camera comes to increase in size.